What is the purpose of bending the toe of the fin towards the knee?

Bending the toe of the fin towards the knee serves to stretch the muscles, particularly those in the lower leg and foot. This positioning can help optimize the fin's performance by allowing a better range of motion when kicking, leading to a more effective swim technique. Flexible fins that can bend in this manner enable divers to generate more propulsion with each kick, which can ultimately enhance their swimming efficiency.

While the movement might influence other factors such as drag or speed, the primary physiological benefit focuses on muscle stretching and improving their overall kicking mechanics. This can directly contribute to more comfortable and efficient swimming, especially over longer distances.